As the demand for wireless communication continues to increase, wireless communication devices such as cellular telephones, personal digital assistants (PDAs), smart handheld devices including Smartphones, laptop computers, tablet computers, etc., are increasingly being equipped with multiple radio transceivers. A multiple radio terminal (MRT) may simultaneously include a Long-Term Evolution (LTE) or LTE-Advanced (LTE-A) radio, a Wireless Local Area Network (WLAN, e.g., WiFi) access radio, and a Bluetooth or Bluetooth Low Energy (BLE) radio. Due to radio spectrum regulation, different technologies may operate in overlapping or adjacent radio spectrums. For example, LTE/LTE-A Time Division Duplex (TDD) mode (Band 40) often operate at 2.300-2.400 GHz, WiFi often operate at 2.400-2.483.5 GHz, and Bluetooth or BLE often operate at 2.402-2.480 GHz.
Simultaneous operation of multiple radio modules co-located on the same physical device, however, can suffer significant degradation including significant interference between them because of the overlapping or adjacent radio spectrums. Due to physical proximity and radio power leakage, when the transmission of data for a first radio module overlaps with the reception of data for a second radio module in time domain, the second radio module reception can suffer due to interference from the first radio module transmission. Likewise, data transmission of the second radio module can interfere with data reception of the first radio module.
FIG. 1 (Prior Art) is a diagram that illustrates interference between a LTE radio module LTE11 and a BLE master radio module BLE12 that are co-located in a multiple radio terminal MRT10. In LTE TDD mode, LTE11 transmits and receives data via scheduled uplink (UL) transmitting and downlink (DL) receiving time slots on a frame-by-frame basis. For example, each LTE frame is 10 ms. For TDD configuration #1, each frame contains a scheduled 2 ms UL for transmitting operation followed by a scheduled 3 ms DL for receiving operation, and so on so forth. On the other hand, for BLE operation, a BLE master and a BLE slave alternate one or more pairs of TX transmission and RX reception during a connection interval. A time inter-frame-spacing (T_IFS) separates each TX and RX operation. For example, each connection interval is 10 ms, and contains two TX-RX pairs. Each T_IFS is 150 us long, and each TX/RX operation ranges from 80-376 us with 1 Mbps data rate. Because LTE11 and BLE12 radio modules are co-located within MRT10, in a general, the transmission of one radio module will interfere with the concurrent reception of another radio module. As illustrated in FIG. 1, data transmission in TX2 of BLE12 interferes concurrent DL data reception of LTE11, and data reception in RX2 of BLE12 is interfered by concurrent UL data transmission of LTE11. Similarly, data transmission in TX4 of BLE12 interferes concurrent DL data reception of LTE11, and data reception in RX4 of BLE12 is interfered by concurrent UL data transmission of LTE11. (Please note that for the purpose of illustration, the time scale of related parts in FIG. 1 is incorrect.)
Filters are often used to mitigate such coexistence interference when there is more than 30 MHz frequency guard band separating the interfering frequencies. Imperfect TX filter design, however, may still result in unacceptable coexistence interference. In addition, to save filtering cost, a pure TDM (Time Division Multiplexing) solution is still preferred, especially when there is only limited frequency guard band. Therefore, the TX/RX timing of a BLE data packet can be aligned with the LTE UL/DL period by selecting an anchor point of the connection interval to prevent coexistence interference.
FIG. 2 (Prior Art) is a diagram that illustrates a TDM solution for preventing coexistence interference between a BLE master device and a co-located LTE radio module. As shown in the top half of FIG. 2, each connection interval contains one TX-RX pair and is 5 ms long for BLE operation, and an anchor point is selected at time t1. For BLE data transmission, the data packet in TX1 is 300 bits long, while the data packet in TX2 is 160 bits long. It can be seen that by selecting the anchor point at t1, there is no coexistence interference for TX1/RX1. However, when the data packet in TX2 becomes shorter, the BLE data reception in RX2 is interfered by the concurrent UL transmission of the collocated LTE radio module. On the other hand, as shown in the bottom half of FIG. 2, each connection interval contains one TX-RX pair and is 5 ms long for BLE operation, and an anchor point is selected at time t2. In this example, the data packet in TX3 is 80 bits long, while the data packet in TX4 is 232-376 bits long. In can be seen that by selecting the anchor point at t2, there is no coexistence interference for TX1/RX1 even for the shortest empty payload packet in TX3. However, when the data packet in TX4 becomes longer, the BLE data transmission in TX4 interferes the concurrent DL reception of the collocated LTE radio module. Therefore, carefully aligning BLE TX/RX with LTE UL/DL may not work as the BLE packet length changes. A solution is sought to prevent coexistence interference between BLE device and collocated LTE radio module effectively.